#include <bits/stdc++.h>
using namespace std;

const int N = 205;

char s[N];

int n;

inline void convert(char &ch) {
    if (ch == 'B') ch = 'W';
    else ch = 'B';
}

bool tryit(char s[], vector<int> &res, char ch) {
    static char t[N];
    strcpy(t, s);
    res.clear();
    for (int i=0; i<n-1; ++i) {
        if (t[i] != ch) {
            res.push_back(i);
            convert(t[i]);
            convert(t[i+1]);
        }
    }
    return t[n-1] == ch;
}

int main(int argc, char const *argv[])
{
    scanf("%d", &n);
    scanf("%s", s);
    vector<int> ans;
    bool suc = tryit(s, ans, 'B');
    if (!suc) suc = tryit(s, ans, 'W');
    if (!suc) puts("-1");
    else {
        printf("%d\n", (int)ans.size());
        for (int i=0; i<ans.size(); ++i) {
            printf("%d%c", ans[i] + 1, i==ans.size()-1? '\n' : ' ');
        }
    }
    return 0;
}
